1. Field of the Invention
The present invention relates to a sheet material feeding device, which feeds sheet materials such as papers to an image forming device, and to an image forming device which is equipped with the sheet material feeding device.
2. Description of the Related Art
The device illustrated in FIG. 6 is known as a conventional sheet material feeding device for feeding stiff papers (sheet materials) such as postcards, envelopes and the like. (Refer to Japanese Patent Application Laid-Open (JP-A) No. 3-13436.)
A sheet material feeding device 100 has a stacking stand 104 on which sheet materials 102 are stacked. The stacking stand 104 is provided at a cassette 105 which is loaded into an image forming device. The stacking stand 104 is usually urged upward by a coil spring 106 which is disposed between the stacking stand 104 and the bottom plate of the cassette 105.
A feed roller 108 having a segment-shaped end surface (i.e., having a substantially fan-shaped cross-section) is provided above the sheet materials 102. When the feed roller 108 rotates, a circular arc shaped surface 108B thereof abuts the upper surface of an uppermost sheet material 102A of the stacked sheet materials 102, so as to feed out the uppermost sheet material 102A.
A conveying roller pair 110 which is driven by a motor (not shown) is provided at the feeding direction downstream side of the sheet material 102A. The sheet material 102A which has been fed out by the feed roller 108 is nipped by the conveying roller pair 110 and conveyed downstream.
A pair of sheet material separating levers 112 which are swingable about a shaft 114 are provided at the transverse direction sides of the sheet materials 102. (The transverse direction of the sheet materials 102 is the direction orthogonal to the conveying direction thereof.) A height limiting member 116, which abuts the uppermost sheet material 102A and limits the height of the stacked sheet materials 102, projects from the sheet material separating lever 112 so as to be positioned above the stacked sheet materials 102.
When the feed roller 108 rotates and the circular arc shaped surface 108B abuts the top surface of the uppermost sheet material 102A, the circular arc shaped surface 108B pushes the stacked sheet materials 102 and the stacking stand 104 down against the urging force of the coil spring 106. Therefore, a gap is formed between the sheet material 102A which is being fed out and the height limiting member 116. As a result, the sheet material 102A is nipped by the conveying roller pair 110 and is smoothly fed out without any conveying resistance due to friction being generated between the sheet material 102A and the height limiting member 116.
However, as illustrated in FIG. 7, when the feed roller 108 is rotated further such that a segment shaped portion (a non circular arc shaped portion) 108A thereof is oriented downward, i.e., when the circular arc shaped surface 108B is oriented upward, the stacked sheet materials 102 and the stacking stand 104 are pushed upward by the urging force of the coil spring 106. As a result, the trailing end of the sheet material 102A which is being fed press-contacts the height limiting member 116, and the conveying resistance increases. In particular, when the sheet material 102 is stiff, the conveying resistance of the uppermost sheet material 102A markedly increases.
As a result, the conveying force of the conveying roller pair 110 must be made large, and the output of the motor for driving the conveying roller pair 110 must be made large. Accordingly, the motor becomes large, and much electric power is consumed. In particular, when the respective sheet materials 102 are being conveyed upward in a substantially vertical state, the conveying roller pair 110 must have a large conveying force. The increase in the size of the motor and the increase in the amount of power consumed are great drawbacks.